1. Field of the Invention
The present invention relates to a load distribution system for commercial vehicles wherein the inflation and deflation of each air bag of an air suspension system of the vehicle is controlled independently and automatically so as to maintain a desired pressure within each air bag so as to control the load being borne by each air bag and its axle so as to achieve optimum load distribution of the overall vehicle.
2. Background of the Prior Art
Under current United States Department of Transportation regulations, in a typical tractor-trailer combination (18 wheeler) the maximum weight load on the steering axle of the combination is 12,000 pounds, while the dual drive axle load is 34,000 pounds and the dual tandem trailer axle load is also 34,000, and the overall tractor-trailer rig cannot gross over 80,000 pounds combined. Additionally, each tire used on the typical tractor-trailer combination has a maximum load capability of 7,200 pounds so that the tires can support 14,400 pounds on the steering axle, 57,800 pounds on the drive axle and 57,800 pounds on the tandem trailer axle. Clearly, there is excess tire weight support capacity relative to the allowable load capacity on each axle.
Many modern truck and trailer manufacturers are implementing air bag suspension systems into their vehicles, turning away from the more traditional steel spring systems. Air bags tend to be lighter, more reliable, more efficient, have a lower natural frequency so as to produce a smoother and more comfortable ride for driver, vehicle, and cargo alike thereby reducing fatigue and minimizing the risk of damage respectively, and tend to reduce wear and tear on various components of the vehicle, among other benefits of air bag suspension systems. The weight of the vehicle and its load is transferred to the axles and thus the tires via a series of air bags, two air bags per axle. The air bags are pressurized and thereby suspend the weight of the vehicle. Modern air bag systems have appropriate sensors and leveling valves that work together to allow the chassis of the vehicle to remain level as the weight shifts as well as to remain at an optimal ride height. Modern air bag suspension systems may also have weight sensors to be able to detect an overload condition on a given axle, issuing an alarm if an overload condition is detected, allowing the operator to take corrective measures.
In an 80,000 pound gross maximum weight configuration for a tractor-trailer rig, as few as twelve 7,200 pound weight supportable tires can be utilized to support the 80,000 gross weight of the overall tractor-trailer combination, which means that more tires are being used on an 18-wheel tractor trailer combination than is required. Such extra tires increase the overall costs of rig operation in that the tires and wheel set themselves cost money to purchase and maintain. Additionally, the additional tires on the rig increase the rolling resistance of the rig which decreases fuel efficiency of the rig.
It would seem obvious to remove some of the tires from the tractor-trailer combination to save the costs associated with using the extra tires while still maintaining the sufficient tire weight bearing capacity required. However, this is not as easy as it seems. The load of the tractor-trailer is not uniform throughout the overall length of the rig, if the load were uniform, then tire removal might be possible. The non-uniform weight distribution on the tractor-trailer means that some axles bear more of the weight than other axles so that if tires were removed from a particular axle and that axle bore more weight for a given load relative to other axles, an over-weight-capacity issue could be created, which can be dangerous.
Therefore, in order to be able to achieve tire removal from a tractor-trailer combination, and realize the attendant savings associated with such tire removal, it is necessary to control the weight distribution at each axle whereat a tire is removed so as to prevent overloading the remaining tires on such axle.
Some prior art systems have been proposed to better distribute weight load on each axle via so-called suspension slider systems. While effective for their intended purpose, such systems are designed to move weight loading onto or away from the tractor depending on the circumstances of a given load. Additionally, such systems are manual in operation and time-consuming to use.
What is needed is a system whereby the weight load imposed on a given axle of a tractor-trailer combination or even a standalone truck such as a dump truck can be controlled so as to allow the removal of one or more of the tires from the vehicle without fear of overloading the axle wherefrom the wheel is removed. Such a system must be automatic in its operation so that vehicle operator or mechanic input is not necessary once the system is properly installed. Such a system should be dynamic so that weight load distribution on the vehicle is automatically adjusted depending on the given conditions of a particular weight load. Ideally, such a system must be relatively inexpensive to produce, install, and maintain.